I propose to study the mechanisms by which astrocytes modulate inhibitory synaptogenesis in the developing central nervous system. Previous work and preliminary studies in hippocampal neurons in vitro show that astrocytes secrete proteins into the media (astrocyte conditioned media, ACM) that increase inhibitory neuron axon length, branching as well as synaptogenesis, by the criteria of increasing the number of GABAergic presynaptic terminals co-localized with postsynaptic GABAAR clusters (Elmariah et al., 2005;Hughes et al., 2005, 2006). These data lead to the hypothesis that astrocyte secreted proteins affect the formation of inhibitory circuitry during neural development. This hypothesis will be tested in three aims: (1) We will complete our studies to determine how astrocyte secreted proteins affect inhibitory axon length, branching and synaptogenesis in 2 experiments. (2) We will continue to use gel filtration and mass spectroscopy to identify astrocyte secreted proteins that increase inhibitory axon length, branching and synaptogenesis. (3) We will test candidate secreted proteins for their role in inhibitory axon length, branching and synaptogenesis. While these aims are high-risk, they are also potentially of very high impact, as very little is known about astrocyte secreted proteins that affect inhibitory neurons. Taken together, these experiments will extend our understanding of how inhibitory circuitry is formed during neural development, and may also contribute to understanding of disorders of development such as epilepsy, autism and mental retardation. PUBLIC HEALTH RELEVANCE: I propose to study the signaling mechanisms by which astrocytes, a type of glia in the brain, affect inhibitory neurons and the formation of inhibitory synapses in the developing central nervous system. The proposed experiments will contribute to understanding of disorders of human nervous system development such as epilepsy, autism and mental retardation, disorders with a significant public health impact.